Earth borehole crookedness detection and indication



March 29, 1960 J. J. ARPS EARTH BOREHOLE CROOKEDNESS DETECTION AND INDICATION Filed Aug. 4, 1954 4 Sheets-Sheet 1 J---- 'IIIIIIIIIII/ INVENTOR,

J9 d. H6 5 March 29, 1960 J. J. ARPS 2,930,137

EARTH BOREHOLE CROOKEDNESS DETECTION AND INDICATION Filed Aug. 4, 1954 4 Sheets-Sheet 2 IN VEN TOR. Jfi/V d. 99 5 J. J. ARPS March 29, 1960 2,930,137

EARTH BOREHOLE CROOKEDNESS DETECTION AND INDICATION Filed Aug. 4. 1954 4 Sheets-Sheet 4 INVENTOR, J/QN d. 919 5 1 a m a a 557 7. F m w w 7.? m m wflw m FM M7 w wf 1 w; a

United States Patent EARTH BOREHOLE CROOKEDNESS DETECTION AND INDICATION Jan I. Arps, Dallas, Tex.

Application August 4, 1954, Serial No. 447,810

12 Claims. (Cl. 33-205) It is well known that earth boreholes drilled by conventional drilling apparatus do not, except perhaps in rare instances, extend vertically into the earth, but generally assume varying angles with respect to the vertical, and that rather than being straight, partake of various degrees of curvature. During drilling operations it is customary to interrupt the drilling from time to time in order to measure the inclination of the bore hole with respect to the vertical at the bottom of the hole with an instrument which is lowered inside the drill string. When the angle of inclination approaches a certain maximum value, drilling is generally continued with less weight on the bit in order to prevent an additional increase in the angle of inclination, or to cause the angle of inclination to decrease. It is generally believed by drillers that by holding the angle of inclination of the borehole below a certain maximum value, drilling and production troubles such as stuck drill pipe, stuck casing, excessive wear of sucker rods, etc., may be reduced or avoided. It has been discovered, however, that the mere fact that a drill hole is inclined cannot be the only cause of these troubles. For example, a straight borehole inclined at a 15 angle with the vertical apparently does not seem to present any serious drilling or production problems. On the other hand, a hole inclined at an angle of only 3 may cause serious difiiculties if the direction of inclination has shifted abruptly from one direction to an opposite direction. It appears therefore, that not the degree of inclination, but rather the crookedness of the borehole, should be limited to some maximum allowable value to obtain a trouble-free operation condition. The crookedness of the bore hole at any depth may be defined as the curvature of the hole at that depth and is indicated by noncoincidence of the borehole axis with a straight line. The curvature is proportional to the ratio of the angle between the tangents to the hole axis at two points a relatively small distance apart and the depth interval or distance between those two points. in other words, the curvature is proportional to the rate of change of the over-all inclination angle, with respect to depth. The over-all angle is neither the angle with respect to the vertical, that is, the vertical angle, nor the horizontal angle, but a combination of both. Accordingly, it would appear possible to determine the change of the over-all angle by measuring the angle of borehole deviation from the vertical and the horizontal angle measured from a given reference direction as, for example, north, at two points in a borehole a relatively small distance apart, and combining these measurements by means of a certain mathematical formula. Such may, in fact, actually be done, but the procedure is, however, complicated and subject to involvement of many errors. Additionally, it is evident that it would be impractical to interrupt the process of drilling frequently enough to make the measurements sufliciently close to each other, because of the relatively high cost. Performing such measurements or surveys insufiiciently close to each other would very likely lead to the following serious disadvantages: (a)

2,930,137 Patented Mar. 29, 1960 The measured borehole curvature would be an average over too large a depth interval and it might happen that, although this average would not exceed a certain maximum, the actual borehole curvature could be excessively large over a small portion of the given interval. (b) An indication or warning that a borehole with too great a curvature was being drilled would often be obtained too late because of the large depth interval betweeen locations at which measurements were performed.

It should be understood that a large borehole curvature or deviation is not necessarily dangerous or undesirable if it does not extend over a depth interval of too small extent, because in such a case the play or free space between the hole and a pipe or rod in the borehole (due to the difference in diameters), would allow the pipe or rod to be subjected to a less sharp bend than that of the borehole itself.

It is, accordingly, an object of this invention to provide a method and apparatus for indicating the crookedness of an earth borehole directly and not by computation from its vertical and horizontal components.

It is another object of this invention to provide a method and apparatus for indicating the degree of curvature or crookedness of an earth borehole continuously during continued drilling of the borehole. This eliminates the necessity for removing the drilling equipment and replacing same by the surveying equipment, and concurrently also eliminates any necessity for performing the curvature determination only at times excessively long intervals apart.

It is an additional object of this invention to provide a method and apparatus for determining the crookedness of an earth borehole continuously while drilling the borehole, and for transmitting information relating to the crookedness or curvature of the borehole practically instantaneously to the driller at the upper end of the borehole, that is, at the surface of the earth. This permits the driller, who may be carrying a large amount of weight on the bit in order to increase the speed of drilling, to immediately reduce the amount of weight on the bit if a sudden increase in borehole curvature, or, as it is commonly called, a dog leg, starts, whereby all of the aforementioned dilficulties associated with sharp changes in borehole inclination may be obviated.

Other objects, advantages and features of novelty will be made evident hereinafter in a more detailed disclosure of the preferred form of the invention.

In the accompanying drawings which illustrate preferred embodiments and modes of operation of a system according to the invention, and in which like reference characters designate the same or similar parts throughout the several views:

Figure 1 is a diagrammatic elevational view of the drilling equipment at the surface of the earth and a sectional diagrammatic view of an earth borehole which deviates from the vertical near its bottom, the deviation being exaggerated for illustrative purposes;

Figure 2 is a schematic diagram showing the relationship of the axis of the borehole and of the axis of the drill collar of the drill string close to the drill bit, in Figure 1;

Figure 3 is a partly sectional view in elevation of the lower end of a drill collar in a borehole, and a diagram of the electric circuits employed in a preferred embodiment of apparatus according to the invention, in which the crookedness of the borehole is determined from eccentricity measurements;

Figure 4 is an exaggerated partly sectional view in elevation of the lower end of a drill string as employed in a second embodiment of apparatus according to the invention, in which an indication of the crookedness of a borehole is obtained by means including strain gauges;

Figure 5 is an explanatory drawing illustrating the possibility of existence of a straight drill collar in a crooked borehole;

Figure 6 is a diagram of the electrical circuits relating to and utilized in the second embodiment of apparatus according to the invention;

Figures 7 and 7a are elevational and lateral sectional views respectively, through the lower end of a drill collar employed in a third embodiment of apparatus according to the invention, in which the crookedness,

of the borehole is determined by utilizing movement of a rod or cable;

Figure 8 is a diagram of a detail of the structure shown in Figures 7 and 7a, the portion within the dotted rectangle corresponding to apparatus indicated in the small dotted rectangle in Figure 7;

Figure 9 is a diagrammatic view of one form of signal receiving and recording equipment according to the invention and located outside the borehole and at the surface of the earth; and

Figure 10 is a diagrammatic view of another form of signal receiving and recording equipment at the surface of the earth.

Referring now to the drawings in detail, and more particularly to Figure 1, there is indicated at 2 a conventional drilling derrick disposed over a borehole 4 drilled by means including a drill string 6 com rising a string of drill pipe extending through the borehole and secured to a series of drill collars, the drill string terminating at a conventional drill bit 9 at the lower end of the borehole. The upper end of the drill pipe is attached to and suspended by a kelley 10 which is in turn rotated by a rotary table 8 operated through conventional gearing by a source of power in the draw works 11. The drill string is supported for rotation by a swivel 13 in turn supported by a hook 14 attached to a traveling block 16 which in turn is supported by a crown block 17 and conventional wire rope extending to the draw works 11. A conventional weight indicator of either hydraulic, mechanical or electronic type and mounted above hook 14 may be utilized to measure or indicate the weight of the drill string while driling. A drilling fluid conduit 20 receives drilling fluid from a pump 24 which draws from a supply sump 22 and discharges into the drill string via the rotary swivel in conventional manner. The thus-far enumerated structures, wih the exception of certain apparatus at the lower end of the drill string, may be conventional and of any desired form and are not, per se, of the present invention. They are shown to illustrate the environment of the invention.

Interposed or hydraufically connected in drilling fluid line 20 is a pressure-change detecting device 26 preferably in the form of a pressure transducer, to be hereinafter explained in greater detail. The drilling fluid is used as a pressure-change signal transmission medium as also hereinafter more fully explained. The lower end of the drill string is, as mentioned, provided with a certain number of drill collars 27, the lowest of which, 28, is provided with apparatus for providing a measure or indication of borehole crookedness or curvature, and for transmitting crookedness indicating pressure-change signals in the downwardly flowing stream of drilling fluid therein for transmission to a point outside the borehole. The drill bit 9 may, if preferred, be supported upon a sub attached to the lower drill collar in conventional manner, to, for example, facilitate change of drill bits.

Deep earth boreholes are never perfectly vertical, and for this reason the bottom portion of the borehole diagrammatically depicted in Figure 1 is shown inclined to the vertical direction. The axis of the inclined portion of the borehole near the bottom is assumed to be a straight line, and the lower end of the drill collar 28 is normally maintained at the center of the borehole by the drill bit 9. From an inspection of Figure 1 it will be obvious that some distance above the bit the drill collar 28 will actually be leaning against the low side of the borehole. Consequently even in a straight but inclined borehole the lower portion of the drill collar is not absolutely straight, but is subjected to a certain amount of bending. The bit may be considered as being the hinged end of the drill string, and for this reason the bending moment is small and may be neglected. In other words, a short portion of the drill collar 28 above the drill bit 9 may be considered as substantially straight.

Figure 2 represents diagrammatically the axis of the borehole, and the axis of the drill collar, close to the bottom of the borehole. The two axes are indicated as intersecting at point B which is located at the bit 9. Now if there be considered two points on the drill collar axis designated respectively A and C (see Figure 2), and located on that portion of the collar axis which being close to the bit is essentially straight, and if points A and C are selected in such a way that BC=2BA, it will be seen that the eccentricities of points A and C, respectively, are equal to :2 and e which are the distances between these respective points and the axis of the borehole. BC being a straight line, it is obvious from the geometry of Figure 2 that e ==2e According to the present invention, signals representing e and e,, are generated and combined together into a resultant signal equivalent to e 2e,,. This signal is determined to be zero in a straight hole, and its value is indicative of a measure of crookedness or curvature in a hole which is not straight, within limitations which will hereinafter be more fully explained.

A variety of electrical, mechanical or other means may be used to measure or indicate the eccentricity of points A and C. In the preferred embodiment of the invention hereinafter disclosed more in detail, the eccentricity is measured by electrical means. Referring now to Figure 3, the lower drill collar 28 is insulated from the drilling fluid in the annulus of the borehole by means of an insulating sleeve 32 suitably secured to the drill collar as by vulcanization. Two sets of closely spaced disc-like metal electrodes 36 and 38, 40 and 42 of the so-cafled point type, are disposed on the ouside of the insulating sleeve 32 in contact with the drilling fluid in the annular space. Electrodes 36 and 38 are utilized to measure the eccentricity at a level midway between those electrodes, which point corresponds to point A in Figure 2. Similarly, electrodes 40 and 42 are utilized to measure the eccentricity at the level corresponding to point C of Figure 2. The electrodes are connected by suitable insulated conductors to apparatus sealed in a steel case (not shown) which is mounted in an enlarged portion of the interior bore of the drill collar 28 in such a manner that passage of the drilling fluid is not interrupted. For a clear portrayal of a manner of mounting such steel case in the drill collar, reference may be made to my copending application Serial No. 182,604 filed August 31, 1950, issued as Patent 2,787,759. The apparatus in the steel case is diagrammatically depicted within the dotted rectangle 44 shown at the right-hand side of Figure 3. This apparatus comprises a constant current electric source 46 connected to electrode 36 by a suitable insulated conductor such as 101, and also connected to a noninsulated and relatively remote part of the drill string, such as at 105, by means of insulated conductors 103 and 102. The portion 105 of the drill string at which conductor 102 is connected may be, as indicated in Figure 3, any suitable point whereby current flowing from constant current source 46 proceeds through conductor 101 and electrode 36, on through the drilling fluid in the borehole, through the earth formation and the drilling fluid to an uninsulated part of the drill string above the insulation jacket 32, and through conductors 102 and 103 to return to the source 46. The current thus required to flow from electrode 36 into the borehole creates an electrical potential field in the hole and in the adjacent earth formation, which causes a difference of electrical potential between the electrode 38 and the remote, noninsulated portion 105 of the drilling string to which the latter electrode is also connected through a primary winding 48 of a transformer 50, as indicated. It is well known to those skilled in the art of electrical logging that if electrodes 36 and 38 were ring electrodes concentric with the borehole, the voltage across winding 48 would substantially represent the apparent resistivity of the formation at a point midway between those electrodes. This apparent resistivity is a function of the true formation resistivity, and also of the resistivity of the drilling fluid in the borehole and of the sizes of the borehole and the drill collar. In the present invention, however, the electrodes 36 and 38 are disc, or point, electrodes, and move in circles around the axis of the drill collar when the drill collar is rotated. Since that axis is eccentric with respect to the axis of the borehole, the signal or voltage picked up at electrode 38 is influenced by the varying depth or thickness of the annulus of the drilling fluid between the rotating electrode and the formation making up the wall of the borehole, and will not be constant. This voltage or signal comprises two components, one of which is constant while the other is an alternating voltage of generally sinusoidal wave form. In ranges of formation or drilling fluid resistivity normally encountered in rotary drilling, it can be shown that the change in apparent resistivity when the drill collar is rotated is substantially proportional to the eccentricity of the drill collar axis with respect to the borehole axis. If the borehole axis and the drill collar axis were coincident, the apparent resistivity, as indicated by the voltage picked up by the electrode 38, would be constant throughout each revolution of the drill collar. With the two axes not in coincidence, however, the alternating component of the voltage picked up at electrode 38 is due to the change in resistance offered by the varying thickness of the drilling fluid between the borehole wall and the electrode 38 as the latter rotates. This alternating component of the voltage picked up at 38 is substantially proportional to the eccentricity of the drill collar axis with respect to the borehole axis at a point midway between electrodes 36 and 38. Accordingly, the magnetic flux induced in the core of transformer 50 by the current in primary winding 48 may be used to represent the eccentricity of the borehole at the level A of Figure 2. In this connection it should again be pointed out that in Figure 2, BC=2BA, and BA is taken proportional to the distance between the bottom of the drill bit and a point midway between electrodes 36 and 38 in Figure 3.

Referring again to Figure 3, a second constant current source 54 generates a current of value equal to one-half the current generated by source 46. Source 54 is connected in a circuit similar to that previously described, 42 designating the current electrode and 40 the corresponding voltage pickup electrode. Electrodes 40 and 42 are so situated on the drill collar that a point midway between the two is twice as far from the lower surface of the drill bit as is a point midway between electrodes 36 and 38. Transformer 50 is provided with a second primary winding 56 connected as indicated to electrode 40 and to the remote grounded portion 105 of the drill string. As previously mentioned, the magnetic flux induced in the core of transformer 50 by the alternating current component of the current flowing through primary winding 48 may be taken to be representative of the eccentricity 6 of the point midway between electrodes 36 and 38. Since the strength of the electric field created by the current from source 54 is equal to but one-half the strength of the field created by the current from source 46, the alternating current through primary 56 may be taken to be representative of one-half the eccentricity of a point midway between electrodes 40 and 42 (corresponding to the eccentricity c of point C of Figure 2. Thus, the flux induced in the transformer core by the alternating current through primary 56 may be represented by the expression e /2. Primary windings 48 and 56 are so constructed that their induced magnetic fluxes are in opposition. Hence the resultant flux is represented by the expression e /2-e,,; or, by the expression e 2e As hereinabove indicated, this expression is representative of the crookedness of the borehole; and it may be mathematically shown that this relationship holds true, after a dog leg begins, until the borehole is drilled therebelow to a distance equal to the electrode spacing above the bit (a distance corresponding to AC of Figure 2).

The secondary winding 52 of transformer 50 is connected to a means capable of producing output pulses of electric current at a frequency or repetition rate which is proportional to the magnitude of the input current. Illustrative of such means is a device commercially available in the form of a sealed tube sold under the name Amperite, and diagrammatically illustrated at 111 in Figure 3. Preferably the output of the transformer is amplified by suitable conventional amplifier means prior to being applied to the aforementioned means. As indicated in Figure 3, secondary 52 is connected by conductors 106 and 107 to an amplifier 108 whose output is applied through conductors 109 and 110 to the input terminals of Amperite tube 111. Tube 111 comprises a bimetallic strip 112, a heater element 113, and leads and contacts so arranged that when current is supplied to the input terminals the heater element heats strip 112, causing the latter to bend and break the input circuit at contact 114 and make, or close, an output circuit at contacts and 116. When the output circuit is closed, current flows from a battery 118 through a circuit including a conductor 117, solenoid coil 119, conductor 120, contacts 116 and 115, and conductor 121. Energization of coil 119 by this current causes actuation of an electromagnetically operable valve 122 depicted diagrammatically in Figure 3 and which is interposed in the drilling fluid passage in the drill collar. Valve 122 is adapted when closed to throttle or restrict the downward flow of drilling fluid through the drill string and thus to create a pressurechange signal in the drilling fluid. The solenoid operated valve may be any suitable one of the many types known in the art, or may be of the cone-shaped type disclosed in my copending application Serial No. 182,604 filed August 31, 1950, issued as Patent 2,787,759, and may be similarly installed. Valve 122 forms a signal producing device whereby information obtained by the eccentricity measuring apparatus indicated in dotted line rectangle 44 of Figure 3 may be transmitted to the surface of the earth exterior of the borehole. When current from amplifier 108 causes heating element 113 to heat sufiiciently so that bimetallic strip 112 bends and closes the battery operated circuit of the solenoid operated valve 122, the drilling fluid stream inside the drill string will be temporarily throttled. The resulting increase in pressure is almost immediately detectable at the surface of the earth and is there detected by suitable transducer means. As soon as the bimetallic strip 112 has cooled sufficiently, the circuit through the valve solenoid is opened at contacts 115 and 116 and the input circuit is closed at 114. The valve then restores itself to fully open position, as by means of a conventional valve spring device, and the pressure in the drilling fluid stream in the drill string returns to normal value. The above described cycle of action repeats itself as soon as contact 114 returns to closed position, and current from amplifier 108 passes through heater element 113. -It is evident that the time required for element 113 to heat sufliciently to break contact 114 and to make contact at 115 and 116 (which is the period between two suecessive pressure-change signals in the drilling fluid stream) depends on the magnitude of the current from amplifier 108. In other words, the higher the degree of curvature or crookedness of the borehole, the smaller the intervals between and the higher the frequency of the successive pressure-change signals imposed on the drilling fluid in the drill string. The frequency of the pressure-change signals may readily be determined from an examination of a graphical record produced by a time clock driven graphical recorder 128 connected as indicated in Figure 9 to receive the electrical output of pressure transducer 26 which is hydraulically connected to conduit 20. The output of the pressure transducer is preferably amplified as, for example, by an amplifier 127. From the preceding disclosure it will be evident that if a straight borehole is being drilled there will be transmitted no pressure-change sig nals and the graph produced by recorder 128 will be a simple straight line. Further, it is evident that a substantially straight but slightly deviating borehole will be evidenced by an occasional pip or signal indication on the graph produced by recorder 128. If the bore hole suddenly commences to be crooked, or a dog leg develops, it will be evidenced by an increase in frequency of pips on the record. Thus, by observing the graph produced by recorder 128 the driller is quickly apprised of the development of the crooked borehole and many take corrective measures immediately.

Another embodiment of apparatus suitable for use in the system of the invention operates on the basis of the fact that in a crooked borehole the drill collar is subject to bending, and for this reason the measurement of the crookedness of the hole may be represented by the measurement of bending moments in the drill collar. Referring now to Figure 4 which indicates diagrammatically and to an exaggerated scale the condition when a dog leg is commencing to be formed in a borehole, the drill collar 28 with bit 9 attached to the lower end thereof is subjected to a bending strain. The bending moment is Zero at the bit because the bit acts like a hinged end. The bending moment is maximum at the level PQ where the drill collar contacts the wall of the borehole. The distance between the bit and the point of contact may vary by large amounts, and depends on hole inclination, the weight on the bit, sizes of the hole and drill collar, abruptness of the dog leg, etc. For this reason the crookedness of the hole is not measured by the bending moment at one point of the drill collar, but by an average of the bending moments over the entire length of the lower drill collar. Measurement of this bending moment is performed by a number of strain gauges 66, herein illustrated by example only as four in number, and located each on the same side of the drill collar. Strain gauges of the type employed are well known in the mechanical arts; one type suitable for the purpose is manufactured by the Baldwin Locomotive Works of Eddystone, Pennsylvania. Strain gauges 66 are so connected that their outputs are additive. As the bent drill collar is rotated the strain gauges are subjected to successive compression and tension strains. As a consequence the electrical output or an electrical current flowing through such strain gauges will comprise an alternating component of approximately sinusoidal wave form whose amplitude is a measure of the total strain and so may be taken as an indication of the degree of crookedness of the borehole. It should be noted that in a straight but inclined borehole the drill collar 28 is slightly bent, as shown 'in Figure 1. Consequently, even in a straight borehole the output signal of the strain gauge device would not be zero. It would, however, be small compared to the output signal produced in a crooked borehole. Thus, a perfectly straight borehole does not correspond to a zero output signal from the strain gauges, but rather corresponds to some small value of the signal, which value may be determined experimentally. Figure indicates a hole with a true dog leg,

in which the drill collar 28 is straight; and consequently the output signal of the strain gauge device is, in such case, equal to zero. As, however, the zero output signal does not correspond to a zero degree of borehole crookedness, the crookedness of the hole shown in Figure 5 would still be indicated by the strain gauge device. In other words, crookedness is, when using this modification of the system of the invention, measured from the deviation of the strain gauge output from a certain experimentally established value other than zero.

The electrical circuitry and other appurtenant apparatus used in connection with the strain gauges is diagrammatically indicated in Figure 6. The apparatus may, as was the case with the previously described embodiment of apparatus, be housed in a steel cylinder or other suitable housing in an enlargement of the lower drill collar 28 and is similarly arranged to produce pressure change signals in the drilling fluid stream in the drill string. In Figure 6 numerals 68 designate the resistors of the strain gauges 66 of Figure 5, the resistances of which resistors vary with the strain in the collar. The strain gauge resistors are preferably cemented inside suitable grooves in a covered portion of the drill collar, and are suitably interconnected and connected to appartus in the cylinder by means of insulated conductors. Resistors 68 are connected as parts of a Wheatstone bridge arrangement comprising a plurality of bridge circuits, each composed of a set of resistors, 68, 72, 70 and 74. Resistors 70 preferably are mounted in the aforementioned grooves, beside the corresponding resistors 68, but are not cemented to the drill collar. Thus any temperature variation in the locality of the resistors will have no unbalancing effect on the bridge networks. Referring again to Figure 6, a suitable alternating current source of electricity such as, for example, an A.-C. generator 76 driven by a battery or by a drilling fluid turbine (not shown), is arranged to supply alternating current in parallel to the primary windings 78 of like transformers 106. The secondary windings 80 of these transformers supply current to respective bridge networks through connections as indicated. The end output terminals 86 and 88 of the series-connected bridges are connected through leads 206 and 207 to a suitable amplifier 208, and the output leads 209 and 210 of the amplifier are connected as indicated to the input of an Amperite tube 211 which comprises a bimetallic strip 212 heated by a heating element 213. When current from input lead 209 passes through the normally closed contact 214 to the heating element 213 and from there to lead 210, element 213 heats strip 212 and the latter bends and breaks contact at 214 and establishes. contact between points 215 and 216. When contact is thus made a circuit from a battery 217, through a lead 218, a solenoid 219 and a lead 220, through contact points 215 and 216 and through a conductor 221 is closed. Current then passes through solenoid 219 and thereby actuates a valve diagrammatically indicated at 222. This valve may in all respects be similar to valve 122 and is located in the drilling fluid stream in the bottom drill collar 28 to effect in the manner hereinbefore described a throttling of the drilling fluid flow and creation of a pressure change signal in the drilling fluid in the drill pipe. Since the output signal from terminals 86 and 88 of the series of Wheatstone bridges is equal to the sum total of the output voltages of the several strain gauges, it is also representative of the degree of crookedness of the borehole. Consequently the frequency of successive pressure-change signals in the drilling fluid stream is also representative of the degree of curvature or crookedness at the bottom of the borehole. Detection and indication of the signals, and interpretation of the repetition rate thereof, are similar to like features of the previously described apparatus.

A third form of apparatus suitable for operation in the system according to the invention is illustrated diagrammatically in Figures 7, 7a and 8. With this embodiment of apparatus, an average bending moment is measured over a substantial length of the drill collar. Figures 7 and 7a are longitudinal and lateral sectional views, respectively, taken through a drill collar 28a in which, in addition to the conventional central passageway or bore for the drilling fluid stream, there is provided a special bore 88 as indicated. Mounted in bore 88, whose sidewall serves to restrict lateral or outward motion of any element located therein, and rotated with the drill collar, is a member 90 preferably in the form of a rod or wire of high tensile strength mounted to be freely movable within the confines of the bore. The upper end of member 90 is secured to a portion of the drill collar 28a as by being brazed or welded to a sidewall of a sealed transverse bore in the drill collar as indicated at 92. The lower end of member 90 is secured in an aperture in a small soft iron armature 94, as by means of welding, and may be bent at its lower end to form a hook, all as indicated in the enlarged diagram of Figur- 8. The hook receives the tension of a strong tension spring 96 which is adjustably tensioned by means such as an adjusting nut 97 threaded on the lower end of hook 99 to which the lower end of spring 96 is hooked. Nut 97 bears against a threaded plug 93 secured in the threaded portion of an enlargement of the bore 88. Bore 88 is closed and maintained fluid tight by means of two threaded plugs as indicated. Since bore 88 is eccentric with respect to the axis of the drill collar, it is evident that as the bent drill collar is rotated, the distance between the fixed ends of the assembly 90, 94, 96, 99 will vary, and this variation will be proportional to the bending moment to which the drill collar is subjected. As a result, the amplitude of the alternating motion of the armature 94 may be taken as representative of the degree of borehole crookedness. Apparatus for translating this motion into an electrical signal is located in the enlargement 98 forming the bottom part of the core 88; and is diagrammatically illustrated on exaggerated scale in Figure 8. Soft iron armature 94 forms part of an inverter having a magnetic circuit comprising, in addition to the armature, a pair of air gaps 102 and a U-shaped core 100. During operation of the apparatus the primary 103 of the inverter is energized with direct current furnished by a battery B through a circuit which is closed at switch S. As the lower end of element 90 is raised and lowered in response to elongation and shortening of that part of the drill collar 28a between 92 and nut 97, the reluctance of the magnetic circuit comprising armature 94 and core 100 is varied because of the increase and decrease of the air gaps 102, whereby there is generated in the secondary 106 of the inverter a voltage of approximately sinusoidal wave form and whose amplitude is indicative of the extent of travel of armature 94 and consequently of the strain produced in the drill collar during its rotation while being bent. Secondary 106 of the inverter is connected by means of leads 306 and 307 to an amplifier 308 of suitable construction whose output is fed through leads 309 and 310 to the input elements of an Amperite tube 311 to operate the latter in the manner hereinabove set forth with respect to Amperite tube 111. The output contacts of tube 311 are connected in a series circuit including a battery 317 and a solenoid 319 of a solenoid actuated valve 322 positioned in the drilling fluid stream in the drill collar and adapted in a manner heretofore explained to produce pressure-change signals in the drilling fluid stream. Since the alternating current output of the secondary 106 of the transformer is proportional to the degree of motion of armature 94, it is proportional to the bending to which the drill collar is subjected, and consequently may be used to indicate crookedness of the borehole in the same manner as with the second described form of apparatus. Accordingly, the frequency with which the tube 311 opens and closes its output contacts and the frequency of the resulting pressure changes produced by valve 322 in the drilling fluid stream and detected at the top of the borehole, will there furnish an indication of the crookedness of the borehole. Current may be supplied to the inverter, and its output current conveyed to the Amperite tube in the steel case in the drill collar by way of a multiconductor cable indicated at 151 in Figures 7 and 7a, the cable being suitably insulated and secured in a recess formed in the drill collar as indicated.

While in the preceding description Amperite" tubes were employed as a means of changing magnitude of electric current into frequency of signal pressure changes, it is evident that many other equivalent devices may likewise be employed. The drilling fluid stream in the drill string serves as a transmission medium for the pressure changes constituting the signals from the newly drilled bottom portion of the borehole to a point outside the borehole, generally denoted by the expression at the surface of the earth.

Turning now to the equipment at the surface of the earth, that is, outside the borehole, necessary to detect and record the pressure-change signals transmitted through the drilling fluid stream in the drill string, two embodiments of such apparatus are shown in Figures 9 and 10. In Figure 9 a pressure pickup head or transducer 26 of conventional design is mounted on conduit 20 so as to be in hydraulic communication with the drilling fluid therein. This pressure pickup head may be any one of a number of types well known in the art. One well suited is of the capacitance type and is illustrated on Figure 3a and described on page 9 of Mechanical Measurements by Electrical Methods, by H. C. Roberts, published by Instruments Publishing Co., Pittsburgh, first edition 1946.

The output from transducer 26 is applied through leads and 126 to a recorder 128 of conventional design, preferably by way of a conventional amplifier 127, whereby pressure variations in the drilling fluid stream in conduit 20 are indicated as sense perceptible indications in the form of a graphical record by the recorder. The recorder diagrammatically depicted is operated by clockwork mechanism which moves a strip of graph paper at a uniform rate past the recording pen. Thus a record in the form of a curve or graph 132 will be produced showing a pressure pulse or pip for each of the pressure change signals created by the valve in the drill collar. When the frequency of the pips or pulses on the graph 132 deviates from an experimentally determined value, it serves as a warning to the driller that the crookedness of the borehole is exceeding the allowable minimum and thereupon the driller may take corrective measures, such as reducing the weight on the bit.

A modification of the surface pressure-change detecting and recording mechanism usable in the system according to the invention is shown diagrammatically in Figure 10. In this device the pressure changes in the drilling fluid stream are detected by detecting a change in the weight of the drill string suspended from book 14. The weight supported by hook 14 is measured by a weight detector 137 which may be any one of the many commercially available weight detecting devices now well known in the art. The electrical output from weight detector 137 is applied through leads 140 and 141 to a recorder 145, preferably by way of a conventional amplifier 142. Amplifier 142 may be like or similar to previously mentioned amplifier 127, and recorder 145 may be like or similar to recorder 128. When the pressure on the inside of the drill string increases during a pressure change signal, the steel drill pipe will expand slightly in diameter due to the elastic properties of the pipe. This expansion will take place over the entire length of the drill string exposed to this pressure differential. The ballooning or swelling effect, even though slight, causes a small reduction in the length of the entire drill string, with the result that a portion of the weight of the lower end of the drill string normally supported assets? by the rock below the drill bit will be supported by hook 14. Thus, during the occurrence of each pressure-rise signal, weight detector 137 will produce an increased output which is reflected upon or indicated by the graph formed by recorder 145. As a consequence, recorder 145 will produce a graphical record of the pressure change signals which is similar to that produced by recorder 128 and may be similarly interpreted.

In this specification and the appended claims, the term signal is intended to mean a plurality of pressure changes created in the drilling fluid stream. That is, a signal may be comprised of a series of successive pressure changes of suflicient number to indicate, by change of their frequency of occurrence, a change in the straightness, or crookedness, of the borehole.

From the preceding description and the drawings, it is evident that the invention provides a system for indicating, preferably outside the borehole and at the surface of the earth, the relative crookedness of an earth borehole or deviation of its axis from a straight line by detecting such deviation within the drill string; and that the system further comprises means operable during continued drilling to perform such detecting and to signal the indication of crookedness to means at the surface of the earth by one or more pressure change signals transmitted through the stream of drilling fluid in the drill string, which latter means is effective to create a sense-perceptible indication of the borehole crookedness, preferably in the form of a graphical record. A plurality of different types of apparatus are disclosed in detail. It is evident from consideration of the description and drawings that many modifications and other forms of apparatus conforming to the system of the invention will occur to those skilled in the art. It is accordingly not desired that the invention be limited to the specific details of the apparatus illustrated and described, but what is claimed is:

1. In a system for indicating crookedness of the newly drilled portion of an earth borehole, during drilling thereof by means including a rotary drill string through which a stream of drilling fluid flows under pressure, apparatus comprising: means in the drill string for producing pressure-changes in the drilling fluid stream at a frequency representative of the extent of bending of the lower end of the drill string; means at the top of the borehole including pressure transducer means in hydraulic communication with said stream, for detecting and recording said pressure changes to provide an indication of the crookedness of the borehole.

2. In a system for indicating crookedness of the newly drilled portion of an earth borehole, during drilling thereof by means including a rotary drill string through which a stream of drilling fluid flows under pressure, apparatus comprising: means in the drill string in the borehole for producing an output representative of the degree of bending of the lower end portion of the drill string; and means in the drill string for producing pressure-change signals in the drilling fluid stream at a rate mathematically related to said ouput, for transmission through said stream to the top of the borehole.

3. In a system for indicating at the surface of the earth the relative crookedness of the bottom portion of an earth borehole, during drilling thereof by means including a rotary drill string through which a stream of drilling fluid flows under pressure, apparatus comprising: means in the drill string including means responsive to deviation of the borehole axis from a straight line to produce an electric current of magnitude mathematically related to the extent of such deviation, and means responsive to said electric current to produce in said stream recurrent pressure-changes at a frequency matematically related to the magnitude of said current; and means at the surface of the earth to detect and create a sense-perceptible indication of said pressure changes, indicative of the crookedness of the borehole being drilled.

. 4. A system as defined by claim 3 in which said means to produce an electric current comprises a plurality of strain gauges secured in longitudinal alignment to the drill string.

5. A system as defined by claim 3, in which said means to produce an electric current comprises: a rod mounted in a lower end portion of the drill string and parallel to the axis of the drill string and spaced from such axis and secured at one of its ends to the drill string; and a variable reluctance inverter device whose reluctance is varied by movement of the other end of said rod relative to the drill string in response to rotation of the lower end portion of the drill string bent along a curved portion of borehole.

6. In a system for indicating at the surface of the earth the relative crookedness of the bottom portion of an earth borehole, during drilling thereof by means including a rotary drill string through which a stream of drilling fluid flows under pressure, apparatus comprising: means in the drill string, including means to produce a pair of electric fields in the vicinity of and rotating with the lower end portion of the drill string, means to pick up alternating voltages from said fields proportional to the inclination of the drill string axis from the axis of the borehole, means to combine said voltages to produce a resultant which is of zero value when the borehole axis is straight but of value different from zero value when the borehole axis is crooked, and means to create recurrent pressure-changes in said stream at a rate indicative of the magnitude of said resultant and of said value; and means outside the borehole in hydraulic communication with said stream for creating a sense-perceptible indication of said pressure changes, indicative of crookedness of the bottom portion of the borehole.

7. A system according to claim 6 in which said means to produce a pair of electric fields includes a pair of disc electrodes mounted in longitudinal alignment on the lower portion of the drill string, and two constant-current electric sources for supplying current to said electrodes.

8. In a system for indicating crookedness of the newly drilled portion of an earth borehole, during drilling thereof by means including a rotary drill string through which a stream of drilling fluid flows under pressure, apparatus comprising: means in the drill string for pro ducing in the borehole an output signal representative of the degree of bending of the lower end portion of the drill string; means in the drill string for producing pressure change signals in the said drilling fluid stream hav ing a predetermined relation to said output signal, for transmission through said stream to the top of the borehole; and means adjacent the top of the borehole to detect said pressure change signals and produce in response thereto sense-perceptible signals indicative of said degree of bending.

9. In a system for indicating crookedness of the newlydrilled portion of an earth borehole, during drilling thereof by means including a rotary drill string through which a stream of drilling fluid flows under pressure, apparatus comprising: means in the drill string for producing in the borehole an output signal representative of the degree of deviation from a straight line of the axis of an adjacent portion of the borehole; means in the drill string for producing pressure change signals in the drilling fluid stream having a predetermined relation to said output signal, for transmission through said stream to the top of the borehole to detect said pressure change signals and produce in response thereto sense-perceptible signals indicative of said degree of deviation.

10. In a system for indicating crookedness of the newly-drilled portion of an earth borehole, during drilling thereof, by means including a rotary drill string, apparatus comprising: means carried by the drill string for producing a pair of laterally outwardly extending, longitudinally spaced-apart electric fields which are greatest in one angular direction about said drill string,

said fields being rotatable relative to a surrounding borehole by rotation of said drill string, whereby variation of the distance of said means from the walls of a surrounding borehole during rotation of said drill string, due to any deviation of the axis of said drill string from parallelism with the axis of said borehole results in variation in said electric fields; and means responsive to variations in differences in said electric fields for producing a sense-perceptible signal having a predetermined relation to said differences, whereby said signal is indicative of the magnitude of said deviation of the axis of said drill string from parallelism with said axis of said borehole.

11. In a system for indicating crookedness of the newly-drilled portion of an earth borehole, during drilling thereof, by means including a rotary drill string, apparatus comprising: means carried by the drill string for producing a pair of laterally outwardly extending, longitudinally spaced-apart electric fields which are greatest in one angular direction about said drill string, said fields being rotatable relative to a surrounding borehole by rotation of said drill string, whereby variation of the distance of said means from the walls of the surrounding borehole during rotation of said drill string, due to any deviation of the axis of said drill string from parallelism with the axis of said borehole, results in variation in said electric fields; means carried by said drill string for picking up voltages from said electric fields; and means to compare said voltages.

12. In a system for indicating crookedness of the newly-drilled portion of an earth borehole, during drilling thereof, by means including a rotary drill string,

apparatus comprising: means carried by the drill string for producing a pair of laterally outwardly extending,

longitudinally spaced-apart electric fields which are greatest in one angular direction about said drill string, said fields being rotatable relative to a surrounding borehole by rotation of said drill string, whereby variation of the distance of said means from the walls of the surrounding borehole during rotation of said drill string, due to any deviation of the axis of said drill string from parallelism with the axis of said borehole results in variation in said electric fields; means carried by said drill string for picking up voltages from said electric fields; and means responsive to variations in difierences between said voltages for producing a sense-perceptible signal having a predetermined relation to said differences, whereby said signal is indicative of the magnitude of said deviation of the axis of said drill string from parallelism with said axis of said borehole.

References Cited in the file of this patent UNITED STATES PATENTS 1,746,562 Sounitza Feb. 11, 1930 1,963,090 Iakosky June 19, 1934 2,190,950 Potapenko Feb. 20, 1940 2,303,360 Irwin Dec. 1, 1942 2,329,732 Varney Sept. 21, 1943 2,388,141 Harrington Oct. 30, 1945 2,425,868 Dillon Aug. 19, 1947 2,524,031 Arps Oct. 3, 1950 2,729,784 Fearon Jan. 3, 1956 2,792,637 Seigel May 21, 1957 FOREIGN PATENTS 14,780 Great Britain Apr. 6, 1916 480,110 France June 22, 1916 

